In 1991 the CSNI published the first State-of-the-Art Report on In-Vessel Core Degradation, which was updated to 1995 under the EU 3rd Framework programme. These covered phenomena, experimental programmes, material data, main modelling codes, code assessments, identification of modelling needs, and conclusions including the needs for further research. This knowledge is relevant to such safety issues as in-vessel melt retention of the core, recovery of the core by water reflood, H2 generation and fission product release.
In the following 20 years, there has been substantial progress in understanding, with major experimental programmes finished, such as the integral Phébus FP tests, and others with many tests completed, e.g. QUENCH, on reflooding degraded rod bundles, and LIVE, on melt pool behaviour. A similar situation obtains regarding integral modelling codes such as MELCOR (USA) and ASTEC (Europe) that encapsulate current knowledge in a quantitative way. With the end of the first two phases of the SARNET network of excellence, now continuing in the NUGENIA association, it is timely to take stock of the knowledge gained.
The Cor ... mehreSOAR project, in NUGENIA/SARNET, draws together the experience of 11 European partners with the aim of comprehensively updating the state of the art in core degradation, over the next two years. The review of available data has begun, and this paper as an example indicates recent progress in small-scale tests involving material interactions that provide data to cover the gaps in knowledge identified in the integral tests. This is complemented by detailed examination of post-test samples to elucidate the mechanisms involved. It also considers advances in thermophysical databases necessary to model the formation and relocation to the lower head of the complex corium compositions involved, as well as phenomena related to in-vessel retention. The report will serve as a reference point for ongoing research programmes in NUGENIA, in other EU research projects such as in Horizon2020, and in CSNI, e.g. the Fukushima benchmark BSAF.